Co-Crystalization and In Vitro Biological Characterization of 5-Aryl-4-(5-Substituted-2-4-Dihydroxyphenyl)-1,2,3-Thiadiazole Hsp90 Inhibitors

Abstract

A potential therapeutic strategy for targeting cancer that has gained much interest is the inhibition of the ATP binding and ATPase activity of the molecular chaperone Hsp90. We have determined the structure of the human Hsp90α N-terminal domain in complex with a series of 5-aryl-4-(5-substituted-2-4-dihydroxyphenyl)-1,2,3-thiadiazoles. The structures provide the molecular details for the activity of these inhibitors. One of these inhibitors, ICPD 34, causes a structural change that affects a mobile loop, which adopts a conformation similar to that seen in complexes with ADP, rather than the conformation generally seen with the pyrazole/isoxazole-resorcinol class of inhibitors. Competitive binding to the Hsp90 N-terminal domain was observed in a biochemical assay, and these compounds showed antiproliferative activity and induced apoptosis in the HCT116 human colon cancer cell line. These inhibitors also caused induction of the heat shock response with the upregulation of Hsp72 and Hsp27 protein expression and the depletion of Hsp90 clients, CRAF, ERBB2 and CDK4, thus confirming that antiproliferative activity was through the inhibition of Hsp90. The presence of increased levels of the cleavage product of PARP indicated apoptosis in response to Hsp90 inhibitors. This work provides a framework for the further optimization of thiadiazole inhibitors of Hsp90. Importantly, we demonstrate that the thiadiazole inhibitors display a more limited core set of interactions relative to the clinical trial candidate NVP-AUY922, and consequently may be less susceptible to resistance derived through mutations in Hsp90.

HSP90 Chaperoning in Addition to Phosphoprotein Required for Folding but Not for Supporting Enzymatic Activities of Measles and Nipah Virus L Polymerases

“…Indeed, the two chemically distinct HSP90 inhibitors we used decrease the chance of observing a biological effect related to any "off-target" activity, as reported in the case of 17-DMAG (49,50). Furthermore, the mechanism of action of both drugs is well characterized, as shown by their perfect docking into the ATPase site of HSP90 (44,51).…”

Structural ensemble-based docking simulation and biophysical studies discovered new inhibitors of Hsp90 N-terminal domain

“…A docked pose is judged as a success when it overlapped with that of the crystal structure within 2 Å in the heteroatoms. ( C ) Receiver operating characteristic (ROC) curves from two structures for high-throughput virtual screening in this study are drawn in red (2BYI-A 28 ) and magenta (2YI5-A 29 ). The blue line corresponds to that of 1UYG-A 51 , which was used as the DUD-E benchmark 20 .…”

“…A higher value of LogAUC reflects the early enrichment of the true-positives more faithfully than using the AUC value. Considering faithful pose reproduction and LogAUC, two structures, 2BYI-A (Chain A from Hsp90N with PDB ID of 2BYI) 28 and 2YI5-A 29 , were selected. In 2BYI-A and 2YI5-A, 38% and 39%, respectively, of the reproduced poses were judged as successes.…”

Chemistry, synthesis and progress report on biological activities of thiadiazole compounds - a review

“…A number of aldose thiosemicarbazones could be converted to thiadiazole derivatives by Young and Eyre method 27 . There are two method by which 1, 3, 4-thiadiazole can be prepared from thiocarbazides.…”

“…Thiobezhydrazide is smoothly converted to 2-phenyl-1, 3, 4-thiadiazole by the action of formic acid 27 . Thiobenzhydrazide is form 2, 5-diphenyl-1,3,4-thiadiazole (33) in small amount when warmed in benzene 36 .…”